1. Field of the Invention
The present invention relates to a liquid jet head, a liquid jet apparatus, and a method of manufacturing a liquid jet head in which a piezoelectric body polarized in a direction in parallel to a substrate surface is joined to upper surfaces of side walls of a recess that forms a pressure chamber for inducing thickness shear deformation to discharge liquid.
2. Description of the Related Art
In recent years, an ink jet type liquid jet head for discharging ink droplets on recording paper or the like to render a character or a graphics or for discharging a liquid material on a surface of an element substrate to form a pattern of a functional thin film is used. In such a liquid jet head of this type, ink or a liquid material is supplied from a liquid tank via a supply tube to the liquid jet head, the ink is caused to fill minute space formed in the liquid jet head, and the capacity of the minute space is momentarily reduced according to a drive signal to discharge a liquid droplet from a nozzle which communicates to the minute space.
Many types of a liquid jet head of this kind have been proposed. Among them, a liquid jet head which uses a thickness shear mode of a piezoelectric element is driven with efficiency and densification thereof is possible. For example, Japanese Patent No. 2666087 describes an ink jet head which uses a thickness shear mode of a piezoelectric body. A bottom sheet formed of a piezoelectric material which is subjected to polarization treatment in a direction perpendicular to a plate surface in advance is prepared, and a large number of grooves in parallel to one another are formed in a surface of the bottom sheet using a dicing blade. A drive electrode is formed on a side wall of each groove, and an upper opening of each groove is closed with an insulating upper sheet. When voltage is applied to the electrode and an electric field is applied in a direction orthogonal to the direction of the polarization, shear mode distortion is created in the side wall forming the groove, and the capacity of minute space formed by the groove changes. The change in the capacity causes liquid which fills the groove to be discharged from a nozzle which communicates to the groove.
Japanese Patent Translation Publication No. Hei 02-501467 also describes an ink jet head in which the capacity of minute space is changed using thickness shear deformation of a piezoelectric body. A plate for a pressure chamber is stacked on a plate for adding stiffness to form a pressure chamber which includes a recess. A transducer formed of a piezoelectric plate is placed on an upper end opening of the pressure chamber. The piezoelectric plate is subjected to polarization treatment in a direction in parallel to a plate surface, and the direction of the polarization is reversed at the center of the pressure chamber. Electrodes are formed on a pressure chamber side and on the opposite side (on an outside surface) thereof of the piezoelectric plate. By applying voltage to the electrodes, an electric field is applied in a thickness direction of the piezoelectric plate. By applying the electric field in the thickness direction of the piezoelectric plate, thickness shear stress the direction of which is reversed at the center of the pressure chamber is produced in the piezoelectric plate, and shearing motion is imposed in the piezoelectric plate to be deformed to the recess side or to the opposite side thereof. The shear motion causes ink which fills the pressure chamber to be discharged from an orifice which communicates to the pressure chamber.
Japanese Patent No. 2867437 also describes an ink jet printer head in which the capacity of minute space is changed using thickness shear deformation of a piezoelectric body. A ceramic thin plate is placed on an upper end opening of a recess formed in a channel body to form a channel. The ceramic thin plate has a structure in which piezoelectric ceramic layers polarized in a direction perpendicular to a plate surface and inner electrode layers are stacked in a lateral direction (in a direction of the plate surface). The ceramic thin plate is bonded to upper end portions of side walls of the recess so that the inner electrode layers are situated over both side walls of the recess and at the center of an upper end of the recess. Therefore, the piezoelectric ceramic layers polarized in the direction perpendicular to the plate surface are sandwiched between the inner electrode layer situated at the center of the upper end of the recess and the inner electrode layers situated over the both side walls of the recess, respectively. Voltage is applied to the inner electrode layer at the center of the upper end of the recess and to the inner electrode layers over the both side walls to apply an electric field in a direction orthogonal to the direction of the polarization of the piezoelectric ceramic layers. The electric field applied to the piezoelectric ceramic layers situated on both sides of the center of the upper end of the recess is in the direction of the plate surface of the ceramic thin plate and the direction thereof is reversed at the center of the upper end of the recess. This causes shear deformation in the ceramic thin plate to increase or decrease the capacity of the channel formed of the recess, and ink which fills the channel is discharged.
Japanese Patent Application Laid-open No. Hei 05-50595 also describes an ink jet printer head in which the capacity of minute space is changed using thickness shear deformation of a piezoelectric body. A drive plate in which a piezoelectric member is bonded between non-piezoelectric members is placed at an upper end opening of a body plate having a recess formed therein to form a pressure chamber. The drive plate is formed of a thin plate in which both ends of a thin plate formed of a piezoelectric material are bonded to non-piezoelectric materials. The bonded portions are situated at the center of an upper end of the recess and over side walls of the recess. The width of the non-piezoelectric members over the side walls is the same as the thickness of the side walls, and the non-piezoelectric members at the center have a smaller width. The thin plates formed of the piezoelectric materials on both sides of the center at the upper end of the recess are polarized in the same direction or in opposite directions within a plate surface. A pair of drive electrodes are formed on a back surface on the pressure chamber side and on the opposite front surface of the thin plate formed of the piezoelectric material so as to be opposed to each other. By applying voltage to the pair of the electrodes, an electric field is applied in a direction orthogonal to the direction of the polarization, and the piezoelectric materials undergo shear mode deformation. When the directions of the polarization of the piezoelectric materials on the both sides of the center of the upper end opening of the recess are the same, electric fields in opposite directions are applied to the piezoelectric materials on the both sides, respectively. When the directions of the polarization of the piezoelectric materials on the both sides are opposite, electric fields in the same direction are applied to the piezoelectric materials on the both sides. This causes deformation of the drive plate to the pressure chamber side or to the opposite side thereof, and ink which fills the pressure chamber is discharged from an orifice which communicates to the pressure chamber.
In the ink jet head described in Japanese Patent No. 2666087, the grooves are formed in the surface of the piezoelectric substrate using a dicing blade. The shape of the dicing blade restricts the length of the grooves, and the arrangement pitch and the capacity of the grooves have a strong correlation with the thickness of the side walls formed of the piezoelectric material and the like, and thus, the design flexibility is small. In the ink jet head described in Japanese Patent Translation Publication No. Hei 02-501467, the plurality of strip-like electrodes for adding a polarity other than a drive electrode are formed on the front and back surfaces of the piezoelectric plate. By applying an electric field in the lateral direction along the plate surface, polarization is performed so that the direction thereof is reversed at the center of the pressure chamber. Therefore, a region for the electrodes for the polarization is necessary in the piezoelectric plate, which makes it difficult to form a pressure chamber having a narrow width to densify the arrangement of the ink discharge nozzles. In the ink jet head described in Japanese Patent No. 2867437, when the stacked ceramic is formed, the piezoelectric ceramic materials and the thermistor materials are alternately stacked and then integrally sintered. However, for example, when an ink jet head having a hundred nozzles is formed, it is necessary to stack and sinter two hundred piezoelectric ceramic materials and thermistor materials, which is two times the nozzles. It is difficult to precisely control the nozzle pitch, and thus, materialization of such an ink jet head is impossible in reality. In the ink jet printer head described in Japanese Patent Application Laid-open No. Hei 05-50595, similarly to the case of the above-mentioned Japanese Patent No. 2867437, it is necessary to stack an enormous number of the piezoelectric members and the non-piezoelectric members. Further, when the non-piezoelectric member is formed, it is necessary to alternately stack the thick layers and the thin layers. Materialization of such an ink jet printer head is extremely difficult in reality.